I am glad someone asked, I was just starting to look in to how to do this same task.
I just picked up a few of these. I was wondering the same thing. I found a few circuits on the net. Here is a few:
http://www.uoguelph.ca/~antoon/circ/sensor2.htm
http://www.acroname.com/howto/photor...oresistor.html
Please post back if you come up with anything.
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